feat: add sqlmesh completion spec

[CR-Lough]

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[withfig-bot]

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[withfig-bot]

Overview

src/sqlmesh.ts:

Info:

[withfig-bot]

Hello @CR-Lough,
thank you very much for creating a Pull Request!
Here is a small checklist to get this PR merged as quickly as possible:

• Do all subcommands / options which take arguments include the args property (args: {})?
• Are all options modular? E.g. -a -u -x instead of -aux
• Have all other checks passed?

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[CR-Lough]

I have read the CLA Document and I hereby sign the CLA